Valve control systems for internal combustion engines that provide for early closing, and thus a shorter open time, of a valve are known in the prior art. An example of an electro-hydraulic valve control system is disclosed by Babitzka et al., U.S. Pat. No. 4,466,390. In the Babitzka et al. system, a hydraulic plug is maintained between a cam follower and a piston by a series of springs, wherein the hydraulic plug is connected to a pressure fluid line and to a drain line controlled by a piezoelectric column to open the drain and provide for closing action of the valve under operation of the valve spring. One such piezoelectric column is provided for each valve and they are altogether connected to an electronic control unit, and the electronic control unit signals the piezoelectric column to clamp or unclamp a sliding valve within the drain line for selective opening of the drain.
The Babitzka et al. system is disadvantageous in that the operation of the control system relies on spring pressure to close the drain line, and that the piezoelectric column must clamp the sliding valve in position by frictionally engaging a portion of the valve to hold the valve against pressure created within the hydraulic plug. Foreign substances and materials thus become much more likely to interfere with proper operation of the clamping function of the piezoelectric column. Moreover, the fully extended operational length of the cam follower, hydraulic plug, and piston is set by counteracting springs that include one between the piston and cam follower and another acting on the piston in an opposite direction. Thus, stop elements are required to maintain proper operational length between the cam shaft and valve stem. The result is that the tappet mechanism for transferring reciprocal movement from the cam shaft to the valve is unnecessarily complex and subject to fatigue and failure, as well as is the control system for operation of the drain line. Furthermore, the control system requires that each valve of the internal combustion engine controlled for early closing, such as all of the intake valves, must be independently associated with a piezoelectric column and drain valve, wherein the electronic control unit independently sends signals to the piezoelectric columns depending on engine conditions. Thus, the control system is again increased in complexity without a simple means for varying the open time and closing action of the valves together.
A mechanical-hydraulic control system is also known and disclosed in the German patent DE-OS2926327. Disclosed in the German patent is a system for translating reciprocal movement from a cam shaft to a valve stem by way of a cam follower and piston separated by a hydraulic plug. In this case, the hydraulic plug is connected to a drain to permit early closing of a valve before the valve would normally close under the influence of the cam shaft alone by a rotary slider that is driven from the cam shaft of the engine. The rotary slider is arranged so that its angular position with respect to a predetermined angle or reference position of the cam shaft can be changed within a limited range. This changing of the angular position to the predetermined angle or reference position of the cam shaft makes the early closing time somewhat variable; however, the degree of variance is disadvantageously limited in the German reference by the manner in which the angular position can be changed. Specifically, an eccentric element is used to act against a transfer element drivingly connected between the cam shaft and the rotary slider. This allows for only a small degree of change of the angular position of the rotary slider.
Moreover, the control system and valve device of the German patent are disadvantageous for the same reasons amplified above with respect to the Babitzka et al. patent, because the valve control depends on at least two springs which maintain the spacing of the hydraulic plug by spacing the cam follower and piston from one another, as well as requiring stop positional elements for the piston. The resultant structure is unnecessarily complex for the translation of reciprocal movement, and is insufficiently variable with respect to timing of the early closing of the valve in each cycle.
In another variable valve lifter arrangement disclosed in U.S. Pat. No. 3,817,228 to Bywater, a control unit is described with a piston and a sliding cylinder, wherein fluid flow from a space between the cylinder and piston is regulated to vary the length of the lifter The lifter device, however, does not provide for early closing of the valve but allows the lift to be varied. This disadvantageously reduces the entire open area of the valve and limits the opening for a sufficient amount of air fuel mixture to pass through.
Other hydraulic valve tappet mechanisms having the ability to compensate tappet length with regard to specific engine characteristics are also known in the prior art. These type devices generally include a movable tappet having a movable piston portion slidable therein with a hydraulic fluid reservoir operatively between the piston and tappet. Functionally, these devices rely on the pressure of hydraulic fluid provided within the space and any accompanying bleeder or drain passages, wherein different pressures of the hydraulic fluid provide for different length adjustments of the tappet mechanism assembly. For instance, in U.S. Pat. No. 3,921,609 to Rhoads, the tappet mechanism utilizes an oil bleed passageway leading to the pressure chamber of the tappet to prevent the lifter from pumping up to a fully solid condition at low speeds; however, the passageway is designed narrow enough to become substantially inoperative at high speeds to produce effectively solid lifter action. In U.S. Pat. No. 4,291,652 to Trzoska, a hydraulic reservoir within the tappet is provided in communication with pressure oil ports such that the pressure chamber selectively is closed or open to the reservoir, wherein the closing or opening of the pressure chamber is controlled by the relative positions of a cylinder and lower piston. U.S. Pat. No. 4.164,917 to Glasson provides a hydraulic tappet with a lash adjustment, as is common in practically all hydraulic tappets, and which further is designed to respond to a control pressure supplied to a hydraulic reservoir depending on whether the internal combustion engine is operated at a power mode or a braking mode. None of these hydraulic tappet mechanisms, however, can operate to open a valve to an operating length and then shorten the open time by permitting an early closing of the hydraulic tappet. Moreover, there is no means to permit a hydraulic link or reservoir to cause an early collapse of the tappet mechanism during a cycle.
In short, the prior art has failed to show a simple and highly accurate means to control a valve tappet mechanism without the need for complex spring and stop arrangements and that can quickly respond to variations in valve closing timing responsive to changing engine conditions. Moreover, the prior art has failed to show a control system that can vary the open time of the tappet mechanism over a relatively wide range of closing times, while also being able to control the timing of all of the tappet mechanisms associated with each cylinder of an internal combustion engine by a single operation.